Although smoking may cause serious respiratory diseases and cancer, it remains extremely difficult for smokers to quit smoking completely.
The active ingredient in a cigarette is nicotine. During smoking, nicotine, along with tar aerosol droplets, enter the smoker's alveolus and are widely absorbed. The nicotine then affects the receptors of the smoker's central nervous system.
Nicotine is a kind of alkaloid with low molecular weight. A small dose of nicotine is essentially harmless to human body and its half-life in blood quite short. The major harmful substance in tobacco is tar. Tar in tobacco is composed of thousands of ingredients. Several of these are cancerogenic.
What is needed, therefore, is a cigarette substitute, which can overcome the above shortcomings.